PCM not ready - sensors resetting

[Georgia_Birdman]

I have a 1998 Explorer Eddie Bauer Edition 4.0 V-6. When I tried to get it inspected this week, the emissions test failed with 5 sensors not ready. After driving for about an hour, I plug in my tester with the engine running and it reports only 2 sensors not ready. Both oxygen sensors are ready and the EGR. Once I turn the ignition off and restart the engine, the PCM resets and reports that all 5 sensors are once again not ready. I have checked all the fuses related to the PCM and sensors, and all are good. Does anyone have any idea what is wrong and what I can do to fix it?

 

[Macgiobuin]

Your starter circuit is drawing too much amperage, so that when starting it, there is NO voltage going to the PCM, in effect resetting your PCM's drive cycles. There is a keep alive circuit going to the PCM which you should trace voltage for, while starting (see if the voltage drops while starting); I would also check for a voltage loss while just the headlights with high beams are on. If you lose voltage on that feeder while the headlights are on, you may have a ground wire problem or other corrosion problem in the wiring connection to the starter. It is pin number 55, a yellow wire.

 

[ThreeJs]

I had an issue like this also.

96 EB Explorer: horn suddenly doesn't work.

Problem Solved. Smog.Horn.Fuse

How a rejected smog test fixed my horn problem.
As stated, I have had a problem with my horn not working. Well, I go to get my yearly smog check and my Explorer was rejected due to 5 different incomplete drive cycle indicators.
The smog tech, whom I've known for years, tells me to drive it more since I cleared the codes. Problem was. I never cleared any codes for over a year.
I then remembered that the 20 Amp Maxi fuse in the underhood junction box is for the horn AND PCM memory power. Fuse 11 in the power distribution box.
I had checked that fuse during my first diagnosis and it looked good. I drove back to work, about 1 mile, and pulled the fuse again. It was hard to tell if the fuse was good until I magnified it. Yup..no good. Bought a new 20A maxi fuse from work for about $3 and drove it for 30 mixed driving miles.
Went back to test. Passed no issues and my horn works too!
So. If your horn doesn't work check maxi fuse 11 and your PCM drive cycle status, if you have a scanner. Everytime you shut off the engine the PCM wil clear if the fuse is blown.

 

[Georgia_Birdman]

All my grounds are good, but I have no voltage on pin 55 (PCM Keep Alive). There is no continuity between the large square connector just above the driver side valve cover. Continuity does exist between this connector and the PCM. I am going to bypass that bad wire with a new wire and see if that works.

 

[Georgia_Birdman]

Macgiobuin, thanks so much! It is fixed!!!! I spliced the yellow wire and now the PCM holds all its data when the ignition is powered off. Just beneath the main power distribution box, I cut the old wire and spliced the new one in. After I cut the wire, I pulled the opposite end and about three inches came completely out of the wire bundle. It had been cut or burnt through. I have no idea how it happened, but it is fixed. I will include some pics just encase anyone else has this problem.

 

[Macgiobuin]

Glad to help. Boom! Mic Drop. Haha!